This invention relates generally to the field of disc drive data handling systems, and more particularly, but not by way of limitation, to a method and apparatus for reducing read element power dissipation during a disc drive idle condition to improve operational life of the read element.
Disc drives are data handling systems used to magnetically store and retrieve digital data files. A typical disc drive comprises one or more rigid recording storage discs arranged about a spindle motor for rotation at a constant high speed. A corresponding array of read/write heads are provided to transfer data between tracks defined on the disc surfaces and a host device (such as a computer) in which the disc drive is mounted. The heads are mounted to a rotary actuator and are controllably positioned adjacent the tracks through the application of current to an actuator motor (such as a voice coil motor, VCM).
Present generation disc drives typically employ heads which utilize separate read and write elements. The write element typically has a thin-film inductive coil construction with a write gap placed in close proximity to the recording medium. Input data to be written to a disc are encoded and serialized to generate a series of bi-directional write currents which are applied to the write element. Each change in the polarity of the write current results in a magnetic flux reversal, or flux transition, in the recording medium. Data are recorded along each track at a selected frequency in relation to the presence of a flux transition (a logical 1) or the absence of a flux transition (a logical 0) at regular intervals along the track.
The read element is typically provided from a magneto-resistive (MR) material having a semiconductor construction with very thin internal boundary areas. The MR element is configured to exhibit changed electrical characteristics when subjected to a magnetic field of a selected orientation. During a read operation, the read element is biased using a relatively small bias level (current or voltage), and the selective magnetization of the disc is detected in relation to induced changes in voltage across (or current through) the read element caused by the magnetization pattern along the track.
A phenomenon referred to as electromigration has been increasingly observed in recent generations of MR read elements. Generally, electromigration occurs when atoms from dissimilar, adjacent metal layers migrate, or mingle across the intermediary boundary between the layers. Such migration leads to a detrimental change in the internal configuration and operation of the device. It has been observed that higher operational temperatures and higher bias levels tend to accelerate the electromigration process in an MR read element, leading to degraded performance and a shortened operational life.
With the continuing trend of providing disc drives with ever greater levels of data storage and data rate capabilities, it is contemplated that future generation heads will have ever increasing levels of reader sensitivity and will thus be even more prone to damage from the effects of electromigration. There is therefore a continued need for improvements in the art whereby the operational performance and life of a disc drive reader element can be maintained and extended, and it is to such improvements that the present invention is directed.
In accordance with preferred embodiments, a disc drive data handling system is provided with a head having a read element used to transduce data from a recording surface.
The disc drive is initially operated in an active mode of operation in which data are transferred between the recording surface and a host device in response to a number of host data transfer commands. An operational read bias signal of selected, nonzero magnitude is applied to the read element to transduce data from the recording surface during the active mode.
Once a predetermined, uninterrupted period of time elapses since the most recent host data transfer command, the disc drive switches to an idle mode of operation. The read bias signal is reduced to a second, nonzero magnitude less than the magnitude of the operational read bias signal and used to transduce data from the data recording surface during the idle mode.
Preferably, the disc drive performs a dithering operation during the idle mode so that the disc drive carries out a number of seeks to tracks on the recording surface, and wherein the data transduced by the reduced read bias signal comprises servo data indicative of position of the read element during said seeks.
The operational read bias signal magnitude is preferably selected using specified criteria, such as read error rate or channel quality measurements. The reduced read bias signal magnitude is preferably selected as a predetermined percentage of the operational read bias signal, or by reducing the read bias level while transducing servo data from the recording surface.
These and various other features and advantages, which characterize the claimed invention, will be apparent from a reading of the following detailed description and a review of the associated drawings.